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Abstract

Straight long-range surface plasmon waveguides are demonstrated as biosensors for the detection of cells, proteins and changes in the bulk refractive index of solutions. The sensors consist of 5 μm wide 22 nm thick Au stripes embedded in polymer (CYTOPTM) with microfluidic channels etched into the top cladding. Bulk sensing is demonstrated by sequentially injecting six solutions of different refractive indices in 2 × 10−3 RIU increments; such index steps were detected with a signal-to-noise ratio of ~1000. Selective capture of cells is demonstrated using Au waveguides functionalized with antibodies against blood group A, and red blood cells of group A and O in buffer as positive and negative analyte. Bovine serum albumin in buffer was used to demonstrate protein sensing. A monolayer of bovine serum albumin physisorbed on a carboxyl-terminated self-assembled monolayer on Au was detected with a signal-to-noise ratio of ~300. Overall, the biosensor demonstrated a good capability for detecting bulk changes in solution and for sensing analyte over a very wide range of mass (from cells to proteins). The biosensors are compact, inexpensive to fabricate, and may find use over a wide range of cost-sensitive sensing and detection applications.

Figures (6)

Fig. 1 Sensing device with integrated fluidics: a) schematic of the device placed on the metal base with a Plexiglas jig on top; the volume of the fluidic cell is 20 µL; b) image of the device with fluidics fixed on the metal base.

Fig. 6 Theoretical response of the waveguide due to adlayer formation: a) Modeled loss response of a straight waveguide due to the formation of an adlayer thereon of thickness a and refractive index na = 1.5. b) Distribution of the Ey field component of the LRSPP (ssb0 [3]) mode used for sensing.